Internet Engineering Task Force (IETF) J. Yi
Request for Comments: 7186 LIX, Ecole Polytechnique
Category: Informational U. Herberg
ISSN: 2070-1721 Fujitsu Laboratories of America
T. Clausen
LIX, Ecole Polytechnique
March
April 2014
Security Threats for the Neighborhood Discovery Protocol (NHDP)
Abstract
This document analyzes common security threats of the Neighborhood
Discovery Protocol (NHDP) and describes their potential impacts on
Mobile Ad Hoc Network (MANET) routing protocols using NHDP. This
document is not intended to propose solutions to the threats
described.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7186.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 4
3. NHDP Threat Overview . . . . . . . . . . . . . . . . . . . . 4
4. Detailed Threat Description . . . . . . . . . . . . . . . . . 4 5
4.1. Jamming . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Denial-of-Service Attack . . . . . . . . . . . . . . . . 5
4.3. Eavesdropping and Traffic Analysis . . . . . . . . . . . 6
4.4. Incorrect HELLO Message Generation . . . . . . . . . . . 7
4.4.1. Identity Spoofing . . . . . . . . . . . . . . . . . . 7
4.4.2. Link Spoofing . . . . . . . . . . . . . . . . . . . . 8
4.5. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 8 9
4.6. Message Timing Attacks . . . . . . . . . . . . . . . . . 9
4.6.1. Interval Time Attack . . . . . . . . . . . . . . . . 9 10
4.6.2. Validity Time Attack . . . . . . . . . . . . . . . . 10
4.7. Indirect Channel Overloading . . . . . . . . . . . . . . 10
4.8. Attack on Link Quality Update . . . . . . . . . . . . . . 11
5. Impact of Inconsistent Information Bases on Protocols using
NHDP . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1. MPR Calculation . . . . . . . . . . . . . . . . . . . . . 12
5.1.1. Flooding Disruption due to Identity Spoofing . . . . 12
5.1.2. Flooding Disruption due to Link Spoofing . . . . . . 13
5.1.3. Broadcast Storm . . . . . . . . . . . . . . . . . . . 14
5.2. Routing Loops . . . . . . . . . . . . . . . . . . . . . . 15
5.3. Invalid or Nonexistent Paths to Destinations . . . . . . 15 16
5.4. Data Sinkhole . . . . . . . . . . . . . . . . . . . . . . 16
6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 18
9.1. Normative References . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . 18
1. Introduction
The Neighborhood Discovery Protocol (NHDP) [RFC6130] allows routers
to acquire topological information up to two hops away from
themselves, by way of periodic HELLO message exchanges. The
information acquired by NHDP is used by other protocols, such as the
Optimized Link State Routing Protocol version 2 (OLSRv2) [RFC7181]
and Simplified Multicast Forwarding (SMF) [RFC6621]. The topology
information, acquired by way of NHDP, serves these routing protocols
by detecting and maintaining local 1-hop and 2-hop neighborhood
information.
As NHDP is typically used in wireless environments, it is potentially
exposed to different kinds of security threats, some of which are of
particular significance as compared to wired networks. As radio
signals can be received as well as transmitted by any compatible
wireless device within radio range, there is commonly no physical
protection as otherwise known for wired networks. NHDP does not
define any explicit security measures for protecting the integrity of
the information it acquires; however, it suggests that the integrity
protection be addressed in a fashion appropriate to the deployment of
the network.
This document is based on the assumption that no additional security
mechanism such as IPsec is used in the IP layer, as not all MANET
deployments may be able to accommodate such common IP protection
mechanisms (e.g., because of limited resources of MANET routers).
The document analyzes possible attacks on and misconfigurations of
NHDP and outlines the consequences of such attacks/misconfigurations
to the state maintained by NHDP in each router (and, thus, made
available to protocols using this state).
This document is not intended to propose solutions to the threats
described. [RFC7185] provides further information on how to enable
integrity protection to NHDP, which can help mitigating the threats
described related to identity spoofing.
It should be noted that many NHDP implementations are configurable,
and so an attack on the configuration system (such as [RFC6779]) can
be used to adversely affect the operation of an NHDP implementation.
The NHDP MIB module [RFC6779] might help monitoring some of the
security attacks mentioned in this document. Note that [MGMT-SNAP] provides a
snapshot of OLSRv2-routed MANET management as currently deployed,
while [MANET-MGMT]
contains is intended to provide specific guidelines on
MANET network management, taking into
account management considering the specific nature of MANETs. various MIB modules that
have been written.
2. Terminology
This document uses the terminology and notation defined in
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message Format"
[RFC5444], "Mobile Ad Hoc Network (MANET) Neighborhood Discovery
Protocol (NHDP)" [RFC6130], and "Internet Security Glossary, Version
2" [RFC4949].
Additionally, this document introduces the following terminology:
NHDP router: A MANET router, running NHDP as specified in [RFC6130].
Attacker: A device that is present in the network and intentionally
seeks to compromise the information bases in NHDP routers.
Compromised NHDP router: An attacker that is present in the network
and generates syntactically correct NHDP control messages.
Control messages emitted by a compromised NHDP router may contain
additional information, or omit information, as compared to a
control message generated by a non-compromised NHDP router located
in the same topological position in the network.
Legitimate NHDP router: An NHDP router that is not a compromised
NHDP router.
3. NHDP Threat Overview
NHDP defines a HELLO messages exchange, enabling each NHDP router to
acquire topological information describing its 1-hop and 2-hop
neighbors, and specifies information bases for recording this
information.
An NHDP router periodically transmits HELLO messages using a link-
local multicast on each of its interfaces with a hop-limit of 1
(i.e., HELLOs are never forwarded). In these HELLO messages, an NHDP
router announces the IP addresses as heard, symmetric, or lost
neighbor interface addresses.
An Attacker has several ways of harming this neighbor discovery
process: it can announce "wrong" information about its identity,
postulate nonexistent links, and replay HELLO messages. These
attacks are presented in detail in Section 4.
The different ways of attacking an NHDP deployment may eventually
lead to inconsistent information bases, not accurately reflecting the
correct topology of the MANET. The consequence is that protocols
using NHDP will base their operation on incorrect information,
causing routing protocols to not be able to calculate correct (or
any) paths, degrade the performance of flooding operations based on
reduced relay sets, etc. These consequences to protocols using NHDP
are described in detail in Section 5.
4. Detailed Threat Description
For each threat, a description of the mechanism of the corresponding
attack is given, followed by a description of how the attack affects
NHDP. The impacts from each attack on protocols using NHDP are given
in Section 5.
For simplicity in the description, the examples given assume that
NHDP routers have a single interface with a single IP address
configured. All the attacks apply, however, for NHDP routers with
multiple interfaces and multiple addresses as well.
4.1. Jamming
One vulnerability, common for all protocols operating a wireless ad
hoc network, is that of "jamming", i.e., that a device generates
massive amounts of interfering radio transmissions, which will
prevent legitimate traffic (e.g., control traffic as well as data
traffic) on part of a network. Jamming is a form of interference and
overload with the threat consequence of disruption [RFC4593].
Depending on lower layers, this may not affect transmissions: HELLO
messages from an NHDP router with "jammed" interfaces may be received
by other NHDP routers. As NHDP identifies whether a link to a
neighbor is unidirectional or bidirectional, a routing protocol that
uses NHDP for neighborhood discovery may ignore a link from a jammed
NHDP router to a non-jammed NHDP router. The jammed router (a router
with jammed carrier) would appear simply as "disconnected" for the
unjammed part of the network, which is able to maintain accurate
topology maps.
If a considerable amount of HELLO messages are lost or corrupted due
to collisions caused by a jamming attack, neighbor NHDP routers are
not able to establish links between themselves any more. Thus, NHDP
will present empty information bases to the protocols using it.
4.2. Denial-of-Service Attack
A denial-of-service (DoS) attack can be a result of misconfiguration
of legitimate NHDP routers (e.g., very short HELLO transmission
interval) or malicious behavior of compromised NHDP routers
[ACCT2012], so-called Byzantine routers [RFC4593]. DoS is a form of
interference and overload with the threat consequence of disruption
[RFC4593].
By transmitting a huge amount of HELLO messages in a short period of
time, NHDP routers can increase channel occupation as described in
Section 4.1. Furthermore, a compromised NHDP router can spoof a
large amount of different IP addresses and send HELLOs to its
neighbors to fill their Link/Neighbor Sets. This may result in
memory overflow, and it makes the processing of legitimate HELLO
messages impossible. A compromised NHDP router can also use link
spoofing in its HELLO messages, generating huge 2-hop Sets in
adjacent NHDP routers and therefore potentially a memory overflow.
Moreover, protocols such as SMF and OLSRv2, using the 2-hop
information for multipoint relay (MPR) calculation, may exhaust the
available computational resources of the router if the Neighbor Set
and 2-hop Sets have too many entries.
By exhausting the memory, CPU, and/or channel resources of a router
in a DoS attack or a misconfiguration, NHDP routers may not be able
to accomplish their specified tasks of exchanging 1-hop and 2-hop
neighborhood information, and thereby disturbing the operation of
routing protocols using NHDP.
In some MANETs, the routers are powered by battery. Another
consequence of a DoS attack in such networks is that the power will
be drained quickly by unnecessary processing, transmitting, and
receiving of messages.
4.3. Eavesdropping and Traffic Analysis
Eavesdropping, sometimes referred to as sniffing, is a common and
easy passive attack in a wireless environment. Once a packet is
transmitted, any adjacent NHDP router can potentially obtain a copy,
for immediate or later processing. Neither the source nor the
intended destination can detect this. A malicious NHDP router can
eavesdrop on the NHDP message exchange and thus learn the local
topology. It may also eavesdrop on data traffic to learn source and
destination addresses of data packets, or other header information,
as well as the packet payload.
Eavesdropping does not pose a direct threat to the network or to
NHDP, in as much as that it does not alter the information recorded
by NHDP in its information bases and presented to other protocols.
However, eavesdropping can provide network information required for
enabling other attacks, such as the identity of communicating NHDP
routers, detection of link characteristics, and NHDP router
configuration. The compromised NHDP routers may use the obtained
information to launch subsequent attacks, and they may also share
NHDP routing information with other NHDP or non-NHDP entities.
[RFC4593] would categorize the threat consequence as disclosure.
Traffic analysis normally follows eavesdropping, which is the process
of intercepting messages in order to deduce information from
communication patterns. It can be performed even when HELLO messages
are encrypted (encryption is not a part of NHDP), for example:
o Triggered HELLO messages: an attacker could figure out that
messages are triggered and determine that there was a change of
symmetric neighbors of an NHDP router sending the HELLO (as well
get the frequency).
o Message size: the message grows exactly by x bytes per neighbor.
Depending on which cipher is used for the encryption, some
information about the size could be inferred, and thus the number
of neighbors could be guessed.
[RFC4593] would categorize the threat consequence as disclosure.
4.4. Incorrect HELLO Message Generation
An NHDP router performs two distinct tasks: it periodically generates
HELLO messages, and it processes incoming HELLO messages from
neighbor NHDP routers. This section describes security attacks
involving the HELLO generation.
4.4.1. Identity Spoofing
Identity spoofing implies that a compromised NHDP router sends HELLO
messages, pretending to have the identity of another NHDP router, or
even a router that does not exist in the networks. A compromised
NHDP router can accomplish this by using an IP address, which is not
its own, in an address block of a HELLO message, and associating this
address with a LOCAL_IF Address Block TLV [IJNSIA2010].
An NHDP router receiving that HELLO message from a neighbor will
assume that it originated from the NHDP router with the spoofed
interface address. As a consequence, it will add a Link Tuple to
that neighbor with the spoofed address, and include it in its next
HELLO messages as a heard neighbor (and possibly as a symmetric
neighbor after another HELLO exchange).
Identity spoofing is particularly harmful if a compromised NHDP
router spoofs the identity of another NHDP router that exists in the
same routing domain. With respect to NHDP, such a duplicated,
spoofed address can lead to an inconsistent state up to two hops from
an NHDP router. [RFC4593] would categorize the threat consequences
as disclosure and deception.
Figure 1 depicts a simple example. In that example, NHDP router A is
in radio range of NHDP router C, but not of the compromised NHDP
router X. If X spoofs the address of A, that can lead to conflicts
for a routing protocol that uses NHDP, and therefore for wrong path
calculations as well as incorrect data traffic forwarding.
.---. .---. .---.
| A |----| C |----| X |
'---' '---' '---'
Figure 1
Figure 2 depicts another example. In this example, NHDP router A is
two hops away from NHDP router C, reachable through NHDP router B.
If the compromised NHDP router X spoofs the address of A, NHDP router
D will take A as its 1-hop neighbor, and C may think that A is indeed
reachable through D.
.---. .---. .---. .---. .---.
| A |----| B |----| C |----| D |----| X |
'---' '---' '---' '---' '---'
Figure 2
4.4.2. Link Spoofing
Similar to identity spoofing, link spoofing implies that a
compromised NHDP router sends HELLO messages, signaling an incorrect
set of neighbors. This is sometimes referred to as falsification
[RFC4593], and in NHDP it may take either of two forms:
o A compromised NHDP router can postulate addresses of non-present
neighbor NHDP routers in an address block of a HELLO, associated
with LINK_STATUS TLVs.
o A compromised NHDP router can "ignore" otherwise existing
neighbors by not advertising them in its HELLO messages.
The effect of link spoofing with respect to NHDP are twofold,
depending on the two cases mentioned above:
o If the compromised NHDP router ignores existing neighbors in its
advertisements, links will be missing in the information bases
maintained by other routers, and there may not be any connectivity
for these NHDP routers to or from other NHDP routers in the MANET.
o On the other hand, if the compromised NHDP router advertises
nonexistent links, this will lead to inclusion of topological
information in the information base, describing nonexistent links
in the network (which, then, may be used by other protocols using
NHDP in place of other, existing, links).
[RFC4593] would categorize the threat consequences as usurpation,
deception, and disruption.
4.5. Replay Attack
A replay attack implies that control traffic from one region of the
network is recorded and replayed in a different region at (almost)
the same time, or in the same region at a different time. This may,
for example, happen when two compromised NHDP routers collaborate on
an attack, one recording traffic in its proximity and tunneling it to
the other compromised NHDP router, which replays the traffic. In a
protocol where links are discovered by testing reception, this will
result in extraneous link creation (basically, a "virtual" link
between the two compromised NHDP routers will appear in the
information bases of neighboring NHDP routers). [RFC4593] would
categorize this as a falsification and interference threat with
threat consequences of usurpation, deception, and disruption.
While this situation may result from an attack, it may also be
intentional: if data traffic is also relayed over the "virtual" link,
the link being detected is indeed valid for use. This is, for
instance, used in wireless repeaters. If data traffic is not carried
over the virtual link, an imaginary, useless link between the two
compromised NHDP routers has been advertised and is being recorded in
the information bases of their neighboring NHDP routers.
Compared to incorrect HELLO message attacks described in Section 4.4,
the messages used in replay attacks are legitimate messages sent out
by (non-malicious) NHDP routers and replayed at a later time or
different locality by malicious routers. This makes this kind of
attack harder to be detect and to counteract; integrity checks cannot
help in this case, as the original message's Integrity Check Value
(ICV) was correctly calculated.
4.6. Message Timing Attacks
In NHDP, each HELLO message contains a "validity time" (the amount of
time that information in that control message should be considered
valid before being discarded) and may contain an "interval time"
field (the amount of time until the next control message of the same
type should be expected) [RFC5497].
4.6.1. Interval Time Attack
A use of the expected interval between two successive HELLO messages
is for determining the link quality in NHDP: if messages are not
received within the expected intervals (e.g., a certain fraction of
messages are missing), then this may be used to exclude a link from
being considered as useful, even if (some) bidirectional
communication has been verified. If a compromised NHDP router X
spoofs the identity of an existing NHDP router A and sends HELLOs
indicating a low interval time, an NHDP router B receiving this HELLO
will expect the following HELLO to arrive within the interval time
indicated. If that expectation is not met, the link quality for the
link A-B will be decreased. Thus, X may cause NHDP router B's
estimate of the link quality for the link A-B to fall below the
minimum considered useful, so the link would not be used
[CPSCOM2011]. [RFC4593] would categorize the threat consequence as
usurpation.
4.6.2. Validity Time Attack
A compromised NHDP router X can spoof the identity of an NHDP router
A and send a HELLO using a low validity time (e.g., 1 ms). A
receiving NHDP router B will discard the information upon expiration
of that interval, i.e., a link between NHDP router A and B will be
"torn down" by X. The sending of a low validity time can be caused
by intended malicious behaviors or simply misconfiguration in the
NHDP routers. [RFC4593] would categorize the threat consequence as
usurpation.
4.7. Indirect Channel Overloading
Indirect Channel Overloading is when a compromised NHDP router X by
its actions causes other legitimate NHDP routers to generate
inordinate amounts of control traffic. This increases channel
occupation and the overhead in each receiving NHDP router that
processes this control traffic. With this traffic originating from
legitimate NHDP routers, the malicious device may remain undetected
in the wider network. It is a form of interference and overload with
the threat consequence of disruption [RFC4593].
Figure 3 illustrates Indirect Channel Overloading with NHDP. A
compromised NHDP router X advertises a symmetric spoofed link to the
nonexistent NHDP router B (at time t0). Router A selects X as MPR
upon reception of the HELLO then triggers a HELLO at t1. Overhearing
this triggered HELLO, the attacker sends another HELLO at t2,
advertising the link to B as lost; this causes NHDP router A to
deselect the attacker as MPR, and to send another triggered message
at t3. The cycle may be repeated, where the link X-B is advertised
alternately as LOST and SYM.
MPRs(X) MPRs()
.---. .---. .---. .---.
| A | | A | | A | | A |
'---' '---' '---' '---'
| | | |
| SYM(B) | | LOST(B) |
| | | |
.---. .---. .---. .---.
| X | | X | | X | | X |
'---' '---' '---' '---'
. .
. .
. .
..... .....
. B . . B .
..... .....
t0 t1 t2 t3
Figure 3
4.8. Attack on Link Quality Update
According to NHDP [RFC6130]:
Link quality is a mechanism whereby a router MAY take
considerations other than message exchange into account for
determining when a link is and is not a candidate for being
considered as HEARD or SYMMETRIC. As such, it is a "link
admission" mechanism.
Section 14.4 of NHDP [RFC6130] then lists several examples of which
information can be used to update link quality. One of the listed
examples uses packet exchanges between neighbor routers (as described
in [RFC5444]), e.g., an NHDP router may update the link quality of a
neighbor based on receipt or loss of packets if they include a
sequential packet sequence number.
NHDP does not specify how to acquire link quality updates
normatively; however, attack vectors may be introduced if an
implementation chooses to calculate link quality based on packet
sequence numbers. The consequences of such threats would depend on
specific implementations. For example, if the link quality update is
based on a sequential packet sequence number from neighbor routers, a
compromised NHDP router can spoof packets appearing to be from
another legitimate NHDP router that skips some packet sequence
numbers. The NHDP router receiving the spoofed packets may degrade
the link quality as it appears that several packets have been
dropped. Eventually, the router may remove the neighbor when the
link quality drops below HYST_REJECT.
5. Impact of Inconsistent Information Bases on Protocols using NHDP
This section describes the impact on protocols that use NHDP when
NHDP fails to obtain and represent accurate information, possibly as
a consequence of the attacks described in Section 4. This
description emphasizes the impacts on the MANET protocols OLSRv2
[RFC7181] and SMF [RFC6621].
5.1. MPR Calculation
MPR selection (as used in [RFC7181] and [RFC6621], for example) uses
information about a router's 1-hop and 2-hop neighborhood, assuming
that (i) this information is accurate, and (ii) each 1-hop neighbor
is apt to act as MPR, depending on the willingness it reports. Thus,
a compromised NHDP router may seek to manipulate the 1-hop and 2-hop
neighborhood information in a router so as to cause the MPR selection
to fail, leading to a flooding disruption of traffic control
messages. This can result in incomplete topology advertisement or
can degrade the optimized flooding to classical flooding.
5.1.1. Flooding Disruption due to Identity Spoofing
A compromised NHDP router can spoof the identify of other routers in
order to disrupt the MPR selection, so as to prevent certain parts of
the network from receiving flooded traffic [IJNSIA2010].
In Figure 4, a compromised NHDP router X spoofs the identity of B.
The link between X and C is correctly detected and listed in X's
HELLOs. Router A will receive HELLOs indicating links from B:{B-E},
X:{X-C, X-E}, and D:{D-E, D-C}, respectively. For router A, X and D
are equal candidates for MPR selection. To make sure the X can be
selected as MPR for router A, X can set its willingness to the
maximum value.
.---. .---. .---.
| E |----| D |----| C |
'---' '---' '---'
| | .
| | .
.---. .---. .---.
| B |----| A |----| X |
'---' '---' '---'
spoofs B
Figure 4
If B and X (i) accept MPR selection and (ii) forward flooded traffic
as if they were both B, identity spoofing by X is harmless. However,
if X does not forward flooded traffic (i.e., does not accept MPR
selection), its presence entails flooding disruption: selecting B
over D renders C unreachable by flooded traffic.
.---.
| D |
'---'
|
|
.---. .---. .---. .---. .---.
| X |----| A |----| B |----| C |----| E |...
'---' '---' '---' '---' '---'
spoofs E
Figure 5
In Figure 5, the compromised NHDP router X spoofs the identity of E,
i.e., routers A and C both receive HELLOs from a router identifying
itself as E. For router B, routers A and C present the same neighbor
sets and are equal candidates for MPR selection. If router B selects
only router A as MPR, C will not relay flooded traffic from B or
transiting via B, and router X (and routers to the "right" of it)
will not receive flooded traffic.
5.1.2. Flooding Disruption due to Link Spoofing
A compromised NHDP router can also spoof links to other NHDP routers,
thereby making itself appear as the most appealing candidate to be
MPR for its neighbors, possibly to the exclusion of other NHDP
routers in the neighborhood. (In particular, this can occur if the
compromised NHDP router spoofs links to all other NHDP routers in the
neighborhood, plus to one NHDP router outside the neighborhood.) By
thus excluding other legitimate NHDP routers from being selected as
MPR, the compromised NHDP router will receive and be expected to
relay all flooded traffic (e.g., traffic control messages in OLSRv2
or data traffic in SMF) that it can then drop or otherwise
manipulate.
In the network in Figure 6, the compromised NHDP router X spoofs
links to the existing router C, as well as to a fictitious W. Router
A receives HELLOs from X and B, reporting X: {X-C, X-W}, B: {B-C}.
All else being equal, X appears a better choice for MPR than B, as X
appears to cover all neighbors of B, plus W.
,---. .....
| S | . C .
'---' .....
| .
| .
.---. .---. .---. .---. .---.
| D |----| C |----| B |----| A |----| X |
'---' '---' '---' '---' '---'
.
.
.....
. W .
.....
Figure 6
As router A will not select B as MPR, B will not relay flooded
messages received from router A. The NHDP routers on the left of B
(starting with C) will, thus, not receive any flooded messages from
router A or transiting router A (e.g., a message originating from S).
5.1.3. Broadcast Storm
A compromised NHDP router may attack the network by attempting to
degrade the performance of optimized flooding algorithms so as to be
equivalent to classic flooding. This can be achieved by forcing an
NHDP router into choosing all its 1-hop neighbors as MPRs. In
MANETs, a broadcast storm caused by classic flooding is a serious
problem that can result in redundancy, contention, and collisions
[MOBICOM99].
As shown in Figure 7, the compromised NHDP router X spoofs the
identity of NHDP router B and, spoofs a link to router Y {B-Y} (Y
does not have to exist). By doing so, the legitimate NHDP router A
has to select the legitimate NHDP router B as its MPR in order for it
to reach all its 2-hop neighbors. The compromised NHDP router Y can
perform this identity-and-link spoofing for all of NHDP router A's
1-hop neighbors, thereby forcing NHDP router A to select all its
neighbors as MPR and disabling the optimization sought by the MPR
mechanism.
.---.
| B |
'---'
|
|
.---. .---. .....
| A |----| X | . . . Y .
'---' '---' .....
spoofs B
Figure 7
5.2. Routing Loops
Inconsistent information bases, provided by NHDP to other protocols,
can also cause routing loops. In Figure 8, the compromised NHDP
router X spoofs the identity of NHDP router E. NHDP router D has
data traffic to send to NHDP router A. The topology recorded in the
information base of router D indicates that the shortest path to
router A is {D->E->A}, because of the link {A-E} reported by X.
Therefore, the data traffic will be routed to NHDP router E. As the
link {A-E} does not exist in NHDP router E's information bases, it
will identify the next hop for data traffic to NHDP router A as being
NHDP router D. A loop between the NHDP routers D and E is thus
created.
.---. .---. .---. .---. .---.
| A |----| B |----| C |----| D |----| E |
'---' '---' '---' '---' '---'
|
|
.---.
| X |
'---'
spoofs E
Figure 8
5.3. Invalid or Nonexistent Paths to Destinations
By reporting inconsistent topology information in NHDP, the invalid
links and routers can be propagated as link state information with
traffic control messages and results in route failure. As
illustrated in Figure 8, if NHDP router B tries to send data packets
to NHDP router E, it will choose router A as its next hop, based on
the information about the nonexistent link {A-E} reported by the
compromised NHDP router X.
5.4. Data Sinkhole
With the ability to spoof multiple identities of legitimate NHDP
routers (by eavesdropping, for example), the compromised NHDP router
can represent a "data sinkhole" for its 1-hop and 2-hop neighbors.
Data packets that come across its neighbors may be forwarded to the
compromised NHDP router instead of to the real destination. The
packet can then be dropped, manipulated, duplicated, etc., by the
compromised NHDP router. As shown in Figure 8, if the compromised
NHDP router X spoofs the identity of NHDP router E, all the data
packets to E that cross NHDP routers A and B will be sent to NHDP
router X, instead of to E.
6. Future Work
This document does not propose solutions to mitigate the security
threats described in Section 4. However, this section aims at
driving new work by suggesting which threats discussed in Section 4
could be addressed by deployments or applications.
o Section 4.1: Jamming - If a single router or a small area of the
MANET is jammed, protocols could be specified that increase link
metrics in NHDP for the jammed links. When a routing protocol
such as OLSRv2 uses NHDP for neighborhood discovery, other paths
leading "around" the jammed area would be preferred, and therefore
would mitigate the threat to some extent.
o Section 4.2: DoS - A DoS attack using a massive amount of HELLO
messages can be mitigated by admitting only trusted routers to the
network. [RFC7185] specifies a mechanism for adding Integrity
Check Values (ICVs) to HELLO messages and therefore providing an
admittance mechanism for NHDP routers to a MANET. (Note that
adding ICVs creates a new DoS attack vector, as ICV verification
requires CPU and memory resources.) However, using ICVs does not
address the problem of compromised routers. Detecting compromised
routers could be addressed in new work. [RFC7185] mandates
implementation of a security mechanism that is based on shared
keys and makes excluding single compromised routers difficult;
work could be done to facilitate revocation mechanisms in certain
MANET use cases where routers have sufficient capabilities to
support asymmetric keys.
o Section 4.3: Eavesdropping - [RFC7185] adds ICVs to HELLO messages
but does not encrypt them. Therefore, eavesdropping of control
traffic is not mitigated. Future work could provide encryption of
control traffic for sensitive MANET topologies. Note that, other
than using a single shared secret key, providing encryption of
traffic among a set of neighbors (when that set is potentially
undetermined) is nontrivial, especially without multiplying
overheads. With traffic analysis, attackers could still deduce
the network information like HELLO message triggering and HELLO
message size, even though the HELLO messages are encrypted.
o Section 4.4.2: Link spoofing - [RFC7185] provides certain
protection against link spoofing, but an NHDP router has to
"trust" the originator of a HELLO that the advertised links are
correct. For example, if a router A reports a link to B, routers
receiving HELLOs from A have to trust that B is actually a
(symmetric) neighbor of A. New protocol work could address
protection of links without overly increasing the space and time
overheads. An immediate suggestion for deployments is to protect
routers against being compromised and to distribute keys only to
trusted routers.
o Section 4.5: Replay Attacks - [RFC7185] uses ICVs and timestamps
to provide some protection against replay attacks. It is still
feasible to replay control messages within a limited time. A
suggestion for deployments is to provide time synchronization
between routers. New work could provide time synchronization
mechanisms for certain MANET use cases or specify a mechanism
using nonces instead of timestamps in HELLO messages.
o Section 4.4.1: Identity spoofing; Section 4.6: Message timing
attacks; Section 4.7: Indirect channel overloading; and
Section 4.8: Attack on link quality update - [RFC7185] provides
protection against these attacks, assuming the routers are not
compromised.
7. Security Considerations
This document does not specify a protocol or a procedure. The
document, however, reflects on security considerations for NHDP and
MANET routing protocols using NHDP for neighborhood discovery.
8. Acknowledgments
The authors would like to gratefully acknowledge the following people
for valuable comments and technical discussions: Teco Boot, Henning
Rogge, Christopher Dearlove, John Dowdell, Joseph Macker, and all the
other participants of the IETF MANET working group.
9. References
9.1. Normative References
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March
2009.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011.
9.2. Informative References
[ACCT2012] Jhaveri, R. and S. Patel, "DoS Attacks in Mobile Ad Hoc
Networks: A Survey", Second International Conference on
Advanced Computing & Communication Technologies (ACCT),
January 2012.
[CPSCOM2011]
Yi, J., Clausen, T., and U. Herberg, "Vulnerability
Analysis of the Simple Multicast Forwarding (SMF) Protocol
for Mobile Ad Hoc Networks", Proceedings of the IEEE
International Conference on Cyber, Physical, and Social
Computing (CPSCom), October 2011.
[IJNSIA2010]
Herberg, U. and T. Clausen, "Security Issues in the
Optimized Link State Routing Protocol version 2",
International Journal of Network Security & Its
Applications, April 2010.
[MANET-MGMT]
Nguyen, J., Cole, R., Herberg, U., Yi, J., and J. Dean,
"Network Management of Mobile Ad hoc Networks (MANET):
Architecture, Use Cases, and Applicability", Work in
Progress, February 2013.
[MGMT-SNAP]
Clausen, T. and U. Herberg, "Snapshot of OLSRv2-Routed
MANET Management", Work in Progress, February 2014.
[MOBICOM99]
Ni, S., Tseng, Y., Chen, Y., and J. Sheu, "The Broadcast
Storm Problem in a Mobile Ad Hoc Network", Proceedings of
the 5th annual ACM/IEEE international conference on Mobile
computing and networking, 1999.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007.
[RFC6621] Macker, J., "Simplified Multicast Forwarding", RFC 6621,
May 2012.
[RFC6779] Herberg, U., Cole, R., and I. Chakeres, "Definition of
Managed Objects for the Neighborhood Discovery Protocol",
RFC 6779, October 2012.
[RFC7181] Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
"The Optimized Link State Routing Protocol Version 2", RFC
7181, March April 2014.
[RFC7185] Herberg, U., Dearlove, C., and T. Clausen, "Integrity
Protection for the Neighborhood Discovery Protocol (NHDP)
and Optimized Link State Routing Protocol Version 2
(OLSRv2)", RFC 7185, March April 2014.
Authors' Addresses
Jiazi Yi
LIX, Ecole Polytechnique
91128 Palaiseau Cedex
France
Phone: +33 1 77 57 80 85
EMail: jiazi@jiaziyi.com
URI: http://www.jiaziyi.com/
Ulrich Herberg
Fujitsu Laboratories of America
1240 E Arques Ave
Sunnyvale, CA 94085
USA
EMail: ulrich@herberg.name
URI: http://www.herberg.name/
Thomas Heide Clausen
LIX, Ecole Polytechnique
91128 Palaiseau Cedex
France
Phone: +33 6 6058 9349
EMail: T.Clausen@computer.org
URI: http://www.thomasclausen.org/